A building with two tenant loadcenters. Identical 30 space with 150A 4 pole main circuit breakers except one has the 4 switches connected and on does not.
I am not sure what is going on. What are the 4 poles connected to?
(I did not open and it is not convenient to go back to look.)
Wow.
That could be three phase four wire which allows for either delta or wye loads and single phase line to line and line to neutral loads. But it is not normal practice to fuse or switch the neutral, so that would be strange and probably not compliant with current codes. If the neutral is switched, then the handle tie is required to prevent you from opening the neutral while leaving any of the phase wires hot.
Or it could be two-phase five wire, with four phase lines at 90 degrees to each other, with or without an un-switched neutral. That would be extremely rare and antique, and most likely in the downtown area of a large, old city.
Or it could be fed with two parallel 150A conductors on each phase landing on separate poles and just be plain ordinary 120/240 single phase three-wire. But I would ask why it is being fed with double 150A main breakers instead of something larger. Can the panel really take 300A on the bus?
From those choices, I favor the third one, but more information is needed. In particular, how many insulated buses are in the panel.